I briefly summarize the mapping efforts conducted with the Large Millimeter Telescope (LMT) to uncover how galaxies form. The galaxies discovered have typical star-formation rates of the order of ~100-1000 Msun/yr at z~1-6.  The derived redshift distribution, number counts, luminosity functions and morphological transformation constrain galaxy formation and evolution models of the bright IR emitting sources discovered.  I will also present the case for the next generation extragalactic surveys to be conducted with TolTEC, as part of its Legacy Program. These surveys will tie the dust properties of the luminous infrared galaxy population (>10 Msun/yr) to their optical counterparts with large samples. 

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